This invention relates to a transient suppressor device assembly.
Transient suppressor device assemblies are known, for example, from European Patent Application No. EP-A-O 123 126. Telecommunication systems are commonly protected from transient voltage surges, such as those resulting from lightning, by gas discharge tubes (G.D.T.). FIG. 1 shows a typical configuration where a three terminal device G.D.T. is placed between two telephone lines, A and B and earth. Frequently main distribution frame systems are provided with one three-terminal G.D.T. for each pair of lines.
The G.D.T. has massive current carrying capability but it has three major disadvantages. The first disadvantage is that the device is not fail-safe in the event of overheating. The occurrence of a continuous high current such as might result from a mains contact of the system, causes excessive heating and serious damage to the main distribution frame. Over-temperature fail-safe devices are known from patent disclosures Nos. DE-A 29 11 110, EP-A-O 040 522, and EP-A-O 134 718, for example. Secondly, degradation of the parameters of the G.D.T. cannot be detected. It is possible for the DC spark-over voltage of the device to increase progressively due to a lack of device hermeticity. This problem is solved by the present invention. Thirdly, the device is relatively slow in its operation. The increasing use of semiconductor devices in telecommunication applications has led to situations where the G.D.T. cannot give adequate protection. Semiconductor devices are extremely sensitive to overvoltage conditions and can be destroyed by voltage surges of less than a nanosecond. Semiconductor protection devices have been developed with faster response times than this, which solve the overvoltage problem, but are unable to cope with the large currents (of the order of 5 KA) which protection devices are expected to carry. The present invention provides a small transient suppression device of similar size to a G.D.T., which has fast response and high current carrying capability.